Polymeric sanitary coating system



7 ing as a whole.

1 2,780,564 POLYMERIC SANITARY COATING SYSTEM Daniel M. Gray and George L. Reymann, Sewickley, Pa.,

assignors, by mesne assignments, to American-Marietta Company, Stoner-Mudge C0. Division, Chicago, Ill., a

corporation of Illinois No Drawing. Application April 7, 1954, Serial No. 421,685 25 Claims. (Cl. 117-75) This invention relates to preparing coatings for metal surfaces, particularly interior and exterior metal surfaces of containers for foods, beverages and other products, including closures for such containers. This application is a continuation-in-part of our co-pending application Serial No. 237,493, filed July 18, 1951 (Patent No. 2,675,334), which is a continuation-in-part of our application Serial No. 152,761, filed March 29, 1950 and later abandoned.

Research has been directed for many years to the problem of improving sanitary coatings for food and beverage containers, taking into consideration the many special requirements which must be observed in regardto such coatings. Many special coatings have been developed which have proved satisfactory in some respects, but their use has been limited by deficiencies in other respects. Vinyl halide polymers, for example, have fair thermal stability but poor adherence and solubility characteristics. Copolymers of vinyl chloride and vinyl acetate have better solubility characteristics in the more active solvents, such as ketones and esters, and comparable adherence but poorer thermalv stability. The latter difficulties may be overcome to some extent in the case of vinyl halide polymers and copolymers of vinyl chloride and vinyl acetate, by adding to the copolymer an oleoresinous varnish modifier previously heat treated to such extent that the mixture is compatible in solution but stratifies when baked on a bare or primed metal surface, with the varnish base migrating to said surface to improve the bond (of. Maier Patent No. 2,380,456). However, vinyl halide polymers, and copolymers of vinyl chloride and vinyl acetate, whether or not so oil-modified, are substantially insoluble in aromatic hydrocarbon solvents, which are relatively inexpensive and therefore desirable solvents to use for practical purposes. In accordance with our present invention there is provided a compatible solution of copolymers of vinyl chloride and vinylidene chloride with an oleoresinous modifier in solvents Which can consist entirely of one or a mixture of benzene and higher boiling aromatic hydrocarbon solvents, the solution being stable during prolonged storage but capable of stratification when baked on a primed or unprimed metal substrate, with the modifier migrating towards the substrate to improve the bond with the substrate through molecular orientation while at the same time permitting the vinyl chloride and vinylidene chloride copolymer to migrate toward the exposed surface of the coating. The resultant composite semi-layered coating has a suflicient concentration of vinyl chloride/vinylidene chloride copolymer adjacent the exposed surface to impart superior qualities of chemical resistance and strength to the coating as a whole, and a sufficient concentration of the modifier adjacent the substrate to impart superior qualities of adherence and thermal stability to the coat- The coating of our invention has excellent adherence over a wide range of baking temperatures from as low as 260 F. up to relatively high limits of baking temperatures before thermal decomposition begins, the lower temperatures serving, for example, to protect adjacent lithography, and the higher temperatures permitting quicker bakes. Unmodified vinyl chloride/ vinylidene chloride copolymer coatings, in contrast, are less adherent even at their optimum baking tempera- United sees Patent ture, are poorly adherent at baking temperatures below 2,780,564 Patented Feb. 5, 1957 2 300 F., and have lower maximum baking temperatures. We have found that for the purposes of our present invention the vinyl chloride/vinylidene chloride copolymer must have its weight ratio of vinyl chloride to vinylidene chloride in the copolymer limited to the range between 30/70 to /25, inclusive, in order to retain full solubility of the coating composition in liquid aromatic hydrocarbon solvents (higher ratios of vinylidene chloride tend to reduce solubility in ketones as well as in aromatic hydrocarbon solvents). However, even within said range of proportions it is necessary to control the polymerization conditions, or to purify the copolymer by filtration or otherwise, to ensure that the copolymer in question is substantially free of homopolymers of vinyl chloride and vinylidene chloride respectively, or copolymers thereof outside of the above-stated range of proportions. Moreover, an acceptable copolymer for our purposes must have a specific viscosity within the range of about 0.12 to 0.30, inclusive, as determined at 25 C., using a 0.4% solution of the copolymer in nitrobenzene. A specific viscosity below the stated range results in a relatively brittle coating with poor thermal stability, and above the stated range results in excessively high solution viscosity for our purposes.

An example of a copolymer of vinyl chloride and vinylidene chloride usable in accordance with the invention, hereinafter referred to as copolymer A, ismade as follows: 82 parts of vinyl chloride and 18 parts of vinylidene chloride are placed together in a glass container at 20 C. and exposed, with agitation, to ultraviolet light, such as may be provided with a watt G. E.7 mercury vapor lamp. After 36 to 72 hours of such treatment the resulting mixture of copolymer and unreacted monomers is removed from the container and dried to remove the unreacted monomers. A copolymer of approximately 60% vinyl chloride and 40% vinylidene chloride is obtained, because the vinylidene chloride enters the copolymer at a faster rate than the vinyl chloride. Copolymers with other ratios of vinyl chloride and vinylidene chloride content may be prepared in a like manner by varying the proportions of the starting charges of vinyl chloride and vinylidene chloride. Other methods of producing a usable copolymer may be employed, such as the above method without ultraviolet light but with a catalyst, such as benzoyl peroxide, and, if necessary, with subsequent filtration to remove the homopolymers which are not soluble in aromatic hydrocarbon solvents. An example of a suitable commercially available copolymer of vinyl chloride and vinylidene chloride is Geon 200x20 of B. F. Goodrich Chemical Company, which has a vinyl chloride/vinylidene chloride ratio of substantially 60/40, and is useful for the purposes of the invention, subject to the above-indicated requirements of complete solubility in aromatic hydrocarbon solvents, and range of viscosity. The examples of Geon 200x20 hereinafter referred to are those satisfying the said requirements.

An example of an oleoresinous modifier usable in accordance with the invention, hereinafter referred to as Modifier A, is made as follows: 20 parts of oil-soluble paraphenyl phenol/formaldehyde resin of non-heat hardening type (e. g., Bakelite BR-254) and 20 parts of tung oil, are mixed in an open varnish kettle and heated to'350" F. in about 15 minutes, and are thereafter held at said temperature for an additional period of about 3 hours, to obtain a viscosity of 10-12 seconds at 350 F. (Zahn #3 cup). The exact cooking time is regulated to obtain a base which is compatible in solution with the cooking, it is thinned with 60 parts of xylene, prior to 4 adding it to the vinyl copolymer dissolved in additional The useful range of ratios of the copolymer to the solvent. modifier solids for the purposes of the invention is 95/5 Other examples of modifiers usable in accordance with to /90, with compositions in the range of ratios from the invention, hereinafter known as Modifiers B and C, 90/10 to 25/75, inclusive, having the optimum baked are made as follows: In the case of Modifier B, 20.7 parts 5 film properties. The following Table I shows test reof an unsaturated petroleum hydrocarbon resin (e. g., suits when using varying proportions of Modifier A and Panarez 32l0 of Pan American Refining Corp, which a 60/40 vinyl chloride/vinylidene chloride copolymer has a Gardner color of 9, a softening point of 200220 (sample of Geon 200x) in solutions consisting of P., an iodine number of 230 and an acid number of less by weight of the combined copolymer and modithan 1) and 29.1 parts of a linseed oil modified with 10 her solids, and 75% of xylene. The coating properties pentaerythritoi and maleic anhydride (e. g., Zymol of of such solutions were tested by roller coating such solu- Archer-Daniel-Midlands Company) are heated to about tions on test specimens and baking the filmed coating at 425 F. in minutes and held at that temperature for 325 F. for 7 minutes (except as noted in the more severe 60 minutes. The mixture is then cooled to 350 F. in conditions for. testing thermal stability, as indicated in minutes, and 50.1 parts of xylene are added. In the 15 item (x) of the table), the dry coating weights being 4-5 case of Modifier C, 3.6 parts of a para-tertiary-amyl mg./sq. in. The test specimens were, first, unprimed M:

phenol/formaldehyde resin (e. g., Bakelite BR4036) lb. electrolytic tinplate; second, unprimed steel (blackand 28.6 parts of tung oil are heated to 350 F. in 30 plate); and third, 4 lb. electrolytic tinplate primed with minutes and held at that temperature for three hours. an oicoresinous primer. The solids ratios from /50 The mixture is then immediately mixed with 40.1 parts 20 to 0/100 at the top of Table I, and their corresponding of a 50% solution of an unsaturated petroleum hydrocharacteristics shown below, are parenthesized in order carbon resin (e. g., the above-mentioned Panarez 3 to distinguish them from the 100/0 to /40 solids ratios 210) in xylene. The solution is then diluted with 27.7 and their characteristics, which are not parenthesized. parts of xylene. Table I 100/0 9.5/5 00/10 /20 70/30 00/40 ram) COPOlYmeI Mxhfier A (so/50) 25 15 (10 00 5 05 (2/08 0 (1) Solution properties: Very light Straw Straw Deep straw. Deeper Very deep straw. straw. stra w. (i) Color Very deep (Very deep (Very deep (Very deep (Very deep (Very deep straw). straw). straw). straw). straw). straw).

a2 20 20 17 (ii) Viscosity in seconds (at 80 F., No. 4 Ford cup) (l6) 10 Clear Clear..." Very slight Very slight haze. haze. (iii) Solution clarity (Slight (Very slight (Clear) (Clear) (Clear) (Clear).

haze). haze). (2) Coating properties:

(iv) Dry adhesion (10 percent):

On tinplatc On black-plate On primed tinplate (v) Absence of blush on pasteurization in water at F.

(10 perfect):

On tinplatc On blackplate On primed tinplatc (vi) Adhesion while wet after said pasteurization (10 perfect):

On tinplate On blackplate 6 On primed tinplato & (vii) Flexibility when bent double:

on finplate {Exccllent Excellent." Excellent... Excellent.... Excellent..." Excellent.

(Excellent) (Excellcnt) (Excellent).. (Good). (Fair)....... (Fair). on blackpmte {Excellent... Excellent Exccllcnt.... Exce1lent Excellent. Excellent.

gExcfilleliiztL glxciellleiifln %G0og) .t.... Fair1)1 .t. Fair) Fair). xce on 'xce en lxce en Exec en excellent..." yxcellcnt. Onlmmcd tmplat "{(Excellent) (Exccl1ent)- (Exeellcnt) (Good) (Fair) (F ir). (viii) Fabrication into 28 mm. screw cap:

on tmphte {Fair-Good" E'eel Fxcell Excellent. Excellent... Excellent.

(Excellont) (Excellent).. (Good) (Fair) (Fair) (Fair) O b late {Fair-Good Excellent. Frmllpnt 'Fxr'elle'nt 'Fxoellent Excellent,

p gExcfllent) Excp llenww Go0g) Fairg n n Fair) gain) 0 mm on ime m1 ime on txcellent lxeellgnt on pimedtmplm "{(Exeellent).. (Excellent).. (Good) (Fair) (Fair) (Fain) (ix) Clarity of baked film:

Clear Clear vtlzlry slight Slight haze" Slight haze.

8Z0. Ontmplate (Slight haze) (\gerysgight (Clcar) (Clear) (Clean) 818. Clear Clear Clear Veiry slight Sllghthaze" Slighthaze.

3Z6. on blackplate (Siighi's v ry 1lght (Clear) (Clear) (Clear) (Clear).

3Z9 3Z0 Clear Clear Clear Vary slight Slight haze Slighthaze. 3Z9. Prmedtmpme (slllight) (vherysllght (Clear) (Clear) (Clear) (Clear).

aze 3Z6 (2;) Thermal stability (max. temp. at 10 min. bake before visible decomposition):

On tinplate {300W 310F 320 11" aao r 335n 340F.

---- (340F.).- (360F.)... (370F.) (390F.) (400F.). (Overttltf r. 290]? aoor 320F 325F awn 335F. Onblackplate --{(a40 aeo1 370 12).--- (390F.) (400I 0 mm 320F 330F 340F 350F 360F 370%. onpnmedtmplate (370 12).--. (380 F.).... (380 (390F.) 400 (Ol t;r400

' v I u The following Table H illustrates the efiect of varying the vinyl chloride/vinylidene chloride ratio in the composition of the invention. The copolymers referred to in the table were made and tested as described above in regard to copolymer A except that the charge was varied aromatic hydrocarbon solvents, such as pure and commercial grades of benzene, toluene, xylene, ethyl benzene, and isopropyl benzene, and hi-flash naphtha and Solvesso No. 100 (singly if desired, but preferably 5 mixed), because these solvents are not only suitable for to give the final ratios of vinyl chloride/vinylidene chlothe purpose, but also are relatively inexpensive. Full ride indicated at the head of the table. Modifier A was solubility in solely aromatic hydrocarbon solvents is obmixed with the copolymer in each instance in an 80/20 tained with solids concentrations of copolymer and modiratio of the copolymer to Modifier A on a dry weight fier, when within the various specified limits, as high as solids basis, and the combined copolymer and modifier in 10 50% solids on a dry weight basis in such solvent. By each instance were dissolved at 25% solids concentravarying the said solids concentration from a 15% minition in solvent consisting solely of xylene, except that in mum, viscosities are readily obtainable for coating by the case of compositions in which the copolymer had p, brush, F011, p y and other conventlonal pph a lon vinyl chloride/vinylidene chloride ratios of 20/80 and a More active SOIWH'IS are not 00 and are 30/20, respectively, the copolymer uld ot dissolve 5 ordinarily not desirable because of their higher cost. sufiiciently for coating purposes, I the e of com- However, ketone and ester solvents may be used singly positions having copolymer vinyl chloride/vinylidene or mixed where desired, in total amounts up to 15% by chloride ratios of 30/70 to 75/25, inclusive, the con- Weight of the total solvent, without adverse effect on the stituents did dissolve satisfactorily, and the indicated exproperties of the solution and final coating. For examples of the latter compositions were each dip coated 20 ample, methyl ethyl ketone, methyl isobutyl ketone, cycloon unprimed lb. electrolytic tinplate and baked for hexanone, isophorone, ethyl acetate and butyl propionate minutes at 330 F., except as noted in item (ix) of Table may be used up to said limit, singly or mixed, to

. increase the proportion of solids in the solution at a given Table II Ratio of vinyl chloride/vinylidenc chloride /80 /70 50/50 75/25 80/20 (I) %i% S dl 1 1 b i l i% dt dpolymerinxylene InsoL. Soluble Soluble Insol.

( ompatibility in solution of copolymer and modifier Coating properties:

(iii) Dry adhesion (10 perfect) (iv) Absence of blush on pasteurization in water at 170 F. (10 perfect) (v) Adhesion while wet after said pasteurization (10 perfect) (vi) Flexibility when bent double (vii) Clarity of baked film (viii) Color of baked film (ix) Thermal stability (max. temp. at 10 min. bake before visible decomposition) 10 10 Excellent.... Excellent... Clear lear Pale gold.... Pale gold 3301 830 F....

The modifier of the invention can employ one or a mixture of drying oils, such as tung oil, dehydrated castor oil, and linseed oil modified with maleic anhydride and pentaerythritol (e. g. Zymol) as the drying oils, and one or a mixture of bodying resins of the oil soluble, nonheat hardening type, such as the following: para-phenyl phenol/formaldehyde (Bakelite BR-254), phenolic aldehyde resins (Super-Beckacite 2000, Bakelite 403 6, Varcum 250), unsaturated petroleum hydrocarbon resins (Velsicol AD450, Panarez #3-210), and treated and untreated natural resins (such as Soft Nevillac, and coumarone-indene resin). The range of useful ratios of the drying oil to bodying resin in the modifier is 20/80 to 67/33, inclusive. For example, the use of previously described modifiers A, B and C with Geon 200x20 in solely xylene solvent is illustrated in the following Table III:

Table III (1) Composition:

Modifier Ratio of Goon 200 x 20 to modific Percent solids (modifier and resin) 1. 01

applied to test pieces (2) Compatibility of modifier and resin in solution as evidenced by clarity of solution (10 perfect,

A B C 90/10 90/10 00/10 The solvents usable in accordance with our invention preferably consist entirely of benzene and higher boiling viscosity. Small amounts of up to 2% alcohols may also be used where desired for such purposes as assisting in filtration of the solution.

Pigments, dyes, waxes and other non-reactants may be added to the composition of the invention for decorative purposes and the like, without otherwise materially affecting the significant characteristics of the composition.

Typical illustrative examples of the composition and coating of the invention are as follows, showing various formulations applied in various ways to coat typical useful articles (the stated parts of modifier A, B and C solutions include both the solids and xylene constituents specified hereinabove in the description of the preparation of these modifiers):

Example I.95 parts of a copolymer of vinyl chloride and vinylidene chloride in proportions of 30/70 are dissolved with agitation in 400 parts of benzene, and then 10 parts of the previously described modifier B solution and 3 parts of oil soluble red dye are successively added. When the resulting mixture, which has a total copolymer and modifier solids concentration of 20% and a viscosity of 28 seconds at F. in a #4 Ford viscosity cup, is applied to unprimed aluminum foil by engraved roller at a Wet thickness to yield a dry film weight of 2 milligrams per square inch, and is baked for 2 minutes at 340 B, it yields a tough, adherent, resistant, red-colored film. The coated foil is suitable for subsequent fabrication into foil wrapper for cheese.

Example 11-80 parts of a copolymer of vinyl chloride and vinylidene chloride in proportions of 60/40 are dissolved with-agitation in 270 parts of xylene, and then 50 parts of the said modifier A solution and 25 parts of aluminum pigment are successively added. When the resulting mixture, which has a total copolymer and modifier solids concentration of 25% and a viscosity of 38 seconds at 80 F. in a #4 Ford viscosity cup, is applied to unprimed steel blackplate by roll coater at a wet thickness to yield a dry film weight of 5 milligrams per square inch, and is baked thereon for 15 minutes at 325 F., it yields a tough, adherent, resistant, aluminum-colored film. The coated article is suitable for subsequent fabrication into oil can ends.

Example III.-90 parts of a copolymer of vinyl chloride and vinylidene chloride in proportions of 60/40 are dissolved with agitation in 439 parts of toluene, and then 25 parts of modifier A solution are added. When the resulting mixture, which has a total copolymer and modifier solids concentration of 18% and a viscosity of 17 seconds at 80 F. in a #4 Ford viscosity cup, is sprayed onto oleoresinous primed tinplate can bodies at a wet thickness to yield a dry film weight of 7 milligrams per square inch, and is baked thereon for 10 minutes at 320 F., it yields a tough, adherent, resistant, clear film.

Example IV.-70 parts of a copolymer of vinyl chloride and vinylidene chloride in proportions of 75/25 are dissolved with agitation in a solvent mixture composed of 140 parts of xylene and 83 parts of hi-flash naphtha, and then 57 parts of the previously described modifier C solution and 85 parts of titanium dioxide pigment are successively added. When the resulting mixture, which has a total copolymer and modifier solids concentration of 30% and a viscosity of 130 seconds at 80 F. in a #4 Ford viscosity cup, is applied to unprimed tinplate by roll coater at a wet thickness to yield a dry film weight of 8 milligrams per square inch, and is baked thereon for minutes at 340 F., it yields a tough, adherent, resistant, cream-colored film. The coated tinplate is suitable for subsequent fabrication into closures for glass containers.

Example V .90 parts of a copolymer of vinyl chloride and vinylidene chloride in proportions of 63/37 are dissolved with agitation in a solvent mixture composed of 191 parts of Xylene and 28 parts of Solvesso 100, and then parts of modifier A solution and 0.5 parts of Resinoil Brown Y are successively added. When the resulting mixture, which has a total copolymer and modifier solids concentration of 30% and a viscosity of 90 seconds at 80 F. in a #4 Ford viscosity cup, is applied to oleoresinous primed tinplate by roll coater at a Wet thickness to yield a dry film weight of 4 milligrams per square inch, and is baked thereon for 7 minutes at 325 F., it yields a tough, adherent, resistant, clear film. The coated tinplate is suitable for subsequent fabrication into can ends.

Example VI.-4O parts of a copolymer of vinyl chloride and vinylidene chloride in proportions of 67/33 are dissolved with agitation in 240 parts of xylene, and then 120 parts of modifier B solution and 100 parts of titanium dioxide pigment are successively added. When the resulting mixture, which has a total copolymer and modifier solids concentration of 25% and a viscosity of 100 seconds at 80 F. in a #4 Ford viscosity cup, is applied to unprinted tinplatc by roll coater at a wet thickness to yield a dry film weight of 5 milligrams per square inch, and is baked thereon for 7 minutes at 340 F., it yields a tough, adherent, resistant, buff-colored film. The coated tinplate is suitable for fabrication into metal canisters.

Example Vll.80 parts of a copolymer of vinyl chloride and vinylidene chloride in proportions of 50/50 are dissolved with agitation in 370 parts of toluene, and then 50 parts of modifier A solution and 10 parts of carbon black pigment are successively added. When the resulting mixture, which has a total copolymer and modifier solids concentration or" 20% and a viscosity of 70 seconds at 80 F. in a #4 Ford viscosity cup, is applied to an oleoresinous primed steel container by dipping at a wet thickness to yield a dry film weight of 8 milligrams per square inch, and is baked thereon for 10 minutes at 330 F., it: yields a tough, adherent, resistant, black film on the container.

Example VIII.25 parts of a copolymer of vinyl chloride and vinylidene chloride in proportions of /40 are dissolved with agitation in 188 parts of xylene, and then 187 parts of modifier A solution are added. When the resulting mixture, which has a total copolymer and modifier solids concentration of 25% and a viscosity of 16 seconds at 30 F. in a #4 Ford viscosity cup, is applied to unprimed tinplate by roll coater at a wet thickness to yield a dry film weight of 6 milligrams per square inch, and is baked thereon for 10 minutes at 355 F., it yields a tough, adherent, resistant, transparent gold-colored film. The coated tinplate is suitable for fabrication into can bodies.

While we have described present preferred embodiments of the invention and methods of practicing the same, it will be recognized that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

We claim:

1. A coating composition in which the resin, oil and solvent constituents consist essentially of (I) copolymer selected from copolymers of vinyl chloride and vinylidene chloride in proportions of 30/ to 25, inclusive, and mixtures thereof, and characterized by complete solubility in xylene at 25 solids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25 C. in 0.4% solution in nitrobenzene; (II) solvent of which at least consists of liquid aromatic hydrocarbon material having a boiling point at least as high as benzene, the balance of the solvent consisting of material selected from the group consisting of methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, ethyl acetate, butyl propionate, and mixtures thereof; and (III) an oleoresinous varnish base which consists of drying oil heated with oil-soluble, non-heat hardening varnish resin, which has a drying oil/varnish resin ratio in the range of 20/80 to 67/33, inclusive, and which is compatible in solution in said solvent with the said copolymer constituent but is capable of stratifying toward a metal surface when the composition is filmed on said surface; the combined solids concentration of the copolymer and oleoresinous varnish base in the solvent being in the range of 15 to 50%, inclusive, by weight, and the ratio of the copolymer to the oleoresinous varnish base on a solids basis being in the range of /5 to 10/90, inclusive.

2. A coating composition in which the resin, oil and solvent constituents consist essentially of (I) copolymer selected from copolymers of vinyl chloride and vinylidene chloride in proportions of 30/70 to 75/25, inclusive, and mixtures thereof, and characterized by complete solubility in xylene at 25 solids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25 C. in 0.4% solution in nitrobenzenc; (II) organic solvent consisting substantially entirely of liquid aromatic hydrocarbon material having a boiling point at least as high as benzene; and (HI) an oleoresinous varnish base which consists of drying oil heated with oil-soluble, nonheat hardening varnish resin, which has a drying oil/varnish resin ratio in the range of 20/80 to 67/33, inclusive, and which is compatible in solution in said solvent with the said copolymer constituent but is capable of stratifying toward a metal surface when the composition is filmed on said surface; the combined solids concentration of the copolymer and oleoresinous varnish base in the solvent being in the range of 15 to 50%, inclusive, by weight, and the ratio of the copolymer to the oleoresinous varnish base on a solids basis being in the range of 95/5 to l0/90, inclusive.

3. A coating composition in which the resin, oil and solvent constituents consist essentially of (I) copolymer selected from copolymersof vinyl chloride and vinylidene chloride in proportions of 30/70 to 75/25, in-

elusive, and mixtures thereof, and characterized by complete solubility in xylene at 25% solids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25 C. in 0.4% solution in nitrobenzene; (II) solvent consisting of material selected from the group consisting of benzene, toluene, xylene and mixtures thereof; (III) an oleoresinous varnish base which consists of drying oil heated with oil-soluble, non-heat hardening varnish resin, which has a drying oil/varnish resin ratio in the range of 20/80 to 67/33, inclusive, and which is compatible in solution in said solvent with the said copolymer constituent but is capable of stratifying toward a metal surface when the composition is filmed on said surface; the combined solids concentration of the copolymer and oleoresinous varnish base in the solvent in the range of 15 to 50%, inclusive, by weight, and the ratio of the copolymer to the oleoresinous varnish base on a solids basis being in the range of 95/5 to /90. inclusive.

4. A coating composition in which the resin, oil and solvent constituents consist essentially of (I) copolymer of vinyl chloride and vinylidene chloride in proportions of substantially 60/ 40 and characterized by complete solubility in xylene at 25 solids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25 C. in 0.4% solution in nitrobenzene; (II) organic solvent consisting substantially entirely of liquid aromatic hydrocarbon material having a boiling point at least as high as benzene; and (III) an oleoresinous varnish base which consists of drying oil heated with oil-soluble, non-heat hardening varnish resin, which has a drying oil/varnish resin ratio in the range of 20/ 80 to 67/33, inclusive, and which is compatible in solution in said solvent with the said copolymer constituent but is capable of stratifying toward a metal surface when the composition is filmed on said surface; the combined solids concentration of the copolymer and oleo-resinous varnish base in the solvent being in the range of to 50%, inclusive, by weight, and the ratio of the copolymer to the oleoresinous varnish base on a solids basis being in the range of 95/5 to 10/ 90, inclusive.

5. A coating composition in which the resin, oil and solvent constituents consist essentially of (I) copolymer selected from copolymers of vinyl chloride and vinylidene chloride in proportions of 30/70 to 75/25, inclusive, and mixtures thereof, and characterized by complete solu bility in xylene at 25% solids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25 C. in 0.4% solution in nitrobenzene; (II) organic solvent consisting substantially entirely of liquid aromatic hydrocarbon material having a boiling point at least as high as benzene; and (III) an oleoresinous varnish base which consists of drying oil heated with oil-soluble, nonheat hardening varnish resin, which has a drying oil/ varnish resin ratio in the range of 80 to 67/33, inclusive, which is compatible in solution in said solvent with the said copolymer constituent but is capable of strati fying toward a metal surface when the composition is filmed on said surface, and in which said drying oil is selected from the group consisting of tung oil, dehydrated castor oil and linseed oil, and said varnish resin is selected from the group consisting of phenolic/aldehyde resins, petroleum resins and natural resins; the combined solids concentration of the copolymer and oleoresinous varnish base in the solvent being in the range of 15 to 50%, inclusive, by weight, and the ratio of the copolymer to the oleoresinous varnish base on a solids basis being in the range of 95/5 to 10/90, inclusive.

6. A coating composition in which the resin, oil and solvent constituents consist essentially of (I) copolymer selected from copolymers of vinyl chloride and vinylidene chloride in proportions of 30/70 to 75/25, inclusive, and mixtures thereof, and characterized by complete solubility in xylene at solids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25 C. in 0.4% solution in nitrobenzene; (II) organic solvent consisting substantially entirely of liquid aromatic hydrocarbon material having a boiling point at least as high as benzene; and (III) an oleores'inous varnish base which consists of tung oil heated with oil-soluble, nonheat hardening para-phenyl phenol/formaldehyde resin in substantially equal proportions, which is compatible in solution in said solvent with the said copolymer constituent but is capable of stratifying toward a metal surface when the composition is filmed on said surface; the combined solids concentration of the copolymer and oleoresinous varnish base in the solvent being in the range of 15 to 50%, inclusive, by weight, and the ratio of the copolymer to the oleoresinons varnish base on a solids basis being in the range of 95/5 to 10/90, inclusive.

7. A coating composition in which the resin, oil and solvent constituents consist essentially of (I) copolymer selected from copolymers of vinyl chloride and vinylidene chloride in proportions of 30/ 70 to /25, inclusive, and mixtures thereof, and characterized by complete solubility in xylene at 25 solids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25 C. in 0.4% solution in nitrobenzene; (II) organic solvent consisting substantially entirely of liquid aromatic hydrocarbon material having a boiling point at least as high as benzene; and (III) an oleoresinous varnish base which consists of drying oil heated with 'oil' soluble, nonheat hardening varnish resin, which has a drying oil/ varnish resin ratio in the range of 20/ 80 to 67/33, inclusive, and which is compatible in solution in said solvent with the said copolymer constituent but is capable of stratifying toward a metal surface when the composition is filmed on said surface; the combined solids concentration of the copolymer and oleoresinous varnish base in the solvent being in the range of 15 to 50%, inclusive, by weight, and the ratio of the copolymer to the oleoresinous varnish base on a solids basis being in the range of 10 to 25 7 5, inclusive.

'8. A coating composition in which the resin, oil and solvent constituents consist essentially of (I) copolymer selected from copolymers of vinyl chloride and vinylidene chloride in proportions of 30/ 70 to 75/25, inclusive, and mixtures thereof, and characterized by complete solubility in xylene at 25 solids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25 C. in 0.4% solution in nitrobenzene; (II) organic solvent consisting substantially entirely of liquid aromatic hydrocarbon material having a boiling point at least as high as benzene; and (111) an oleoresinous varnish base which consists of drying oil heated with oil-soluble, Rnheat hardening varnish resin, which has a drying oil/varnish resin ratio in the range of 20/ 80 to 67/33, inclusive, and which is compatible in solution in said solvent with the said copolymer constituent but is capable of stratifying toward a metal surface when the composition is filmed on said surface; the combined solids concentration of the copolymer and oleoresinous varnish base in the solvent being in the range of 15 to 50%, inclusive, by weight, and the ratio of the copolymer to the oleoresinous varnish base on a solids basis being substantially 90/10.

9. A coating composition in which the resin, oil and solvent constituents consist essentially of (I) copolymer of vinyl chloride and vinylidene chloride in proportions of substantially 60/40, characterized by complete solubility in xylene at 25 solids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25 C. in 0.4% solution in nitrobenzene; (II) solvent selected from the group consisting of benzene, toluene, xylene and mixtures thereof; and (III) an oleoresinous varnish base which consists of tung oil heated with oil soluble, non-heat hardening para-phenyl phenol/formaldehyde varnish resin, the oil and resin being in substan- 11 tially equal proportions, and which is compatible in solution in said solvent with. the said copolymer but is capable of stratifying toward a metal surface when the composition is filmed on said surface; the combined solids cncentration of the copolymer and oleoresinous varnish base in the solvent being in the range of 15 to 50%, inelusive, by weight, and the ratio of the copolymer to the oleoresinous varnish base on a solids basis being in the range of 95/5 to /90, inclusive.

10. A coating composition in which the resin, oil and solvent constituents consist essentially of (I) copolymer of vinyl chloride and vinylidene chloride in proportions of substantially 60/40, characterized by complete solubility in xylene at 25% solids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25/ C. in 0.4% solution in nitrobenzene; (II) solvent selected from the group consisting of benzene, toluene, xylene and mixtures thereof; and (III) an oleoresinous varnish base which consists of tung oil heated with oil soluble, non-heat hardening para-phenyl phenol/formaldehyde varnish resin, the oil and resin being in substantially equal proportions, and which is compatible in solution in said solvent with the said copolymer but is capable of stratifying toward a metal surface when the composition is filmed on said surface; the combined solids concentration of the copolymer and oleoresinous varnish base in the solvent being in the range of to 50%, inclusive, by weight, and the ratio of the copolymer to the oleoresinous varnish base on a solids basis being substantially 90/ 10.

11. A process of coating a metal surface comprising the steps of filming on the metal surface a composition in which the resin, oil and solvent constituents consist essentially of (I) copolymer selected from copolymers of vinyl chloride and vinylidene chloride in proportions of 30/ 70 to 75/25, inclusive, and mixtures thereof, and characterized by complete solubility in xylene at 25% solids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25 C. in 0.4% solution in nitrobenzene; (II) solvent of which at least 85% consists of liquid aromatic hydrocarbon material having a boiling point at least as high as benzene, the

balance of the solvent consisting of material selected from the group consisting of methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, ethyl acetate, butyl propionate, and mixtures thereof; and (III) an oleoresinous varnish base which consists of drying oil heated with oil-soluble, non-heat hardening varnish resin, which has a drying oil/varnish resin ratio in the range of /80 to 67/ 33, inclusive, and which is compatible in solution in said solvent with the said copolymer constituent but is capable of stratifying toward a metal surface when the composition is filmed on said surface; the combined solids concentration of the copolymer and oleoresinous varnish base in the solvent being in the range of 15 to 50%, inclusive, by Weight, and the ratio of the copolymer to the oleoresinous varnish base on a solids basis being in the range of 95/5 to 10/90, inclusive; and baking the filmed composition on the metal surface at a temperature of at least 260 F. to form a strong, resist-ant, adherent coating thereon.

12. A process of coating a metal surface comprising the steps of filming on the metal surface a composition in which the resin, oil and solvent constituents consist essentially of (I) copolymer selected from copolymers of vinyl chloride and vinylidene chloride in proportions of 30/70 to 75/25, inclusive, and mixtures thereof, and characterized by complete solubility in xylene at solids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25 C. in 0.4% solution in nitrobenzene; (II) solvent of which at least 85% consists of liquid aromatic hydrocarbon material having a boiling. point at least as high as benzene, the balance of the solvent consisting of methyl ethyl ketone, methyl isobutyl ket-one, cyclohexanone, isophorone, ethyl acetate,

butyl propionate, and mixtures thereof; and (III) an oleoresinous varnish base which consists of drying oil heated with oil-soluble, non-heat hardening varnish resin, which has a drying oil/varnish resin ratio in the range of 20/80 to 67/33, inclusive, and which is compatible in solution in said solvent with the said copolymer constituent but is capable of stratifying toward a metal surface when the composition is filmed on said surface; the combined solids concentration of the copolymer and oleoresinous varnish base in the solvent being in the range of 15 to inclusive, by weight, and the ratio of the copolymer to the oleoresinous varnish base on a solids basis being in the range of 95/5 to 10/90, inclusive; and baking the filmed composition on the metal surface at a temperature in the range of below 300 F. down to 260 F. to form a strong, resistant, adherent coating thereon.

13. A process of coating a metal surface comprising the steps of filming on the metal surface a composition in which the resin, oil and solvent constituents consist essentially of (I) copolymer selected from copolymers of vinyl chloride and vinylidene chloride in proportions of 30/70 to /25, inclusive, and mixtures thereof, and characterized by complete solubility in xylene at 25% olids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25 C. in 0.4% solution in nitrobenzene; (II) solvent of which at least consists of liquid aromatic hydrocarbon material having a boiling point at least as high as benzene, the balance of the solvent consisting of methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, ethyl acetate, butyl propionate, and mixtures thereof; and (III) an oleoresinous varnish base which consists of drying oil heated with oil-soluble, non-heat hardening varnish resin, which has a drying oil/varnish resin ratio in the range of 20/80 to 67/33, inclusive, and which is compatible in solution in said solvent with the said copolymer constituent but is capable of stratifying toward a metal surface when the composition i filmed on said surface; the combined solids concentration of the copolymer and oleoresinous varnish base in the solvent being in the range of 15 to 50% inclusive, by weight, and the ratio of the copolymer to the oleoresinous varnish base on a olids basis being in the range of /10 to 25/75, inclusive; and baking the filmed composition on the metal surface at a temperature of at least 260 F. to form a strong, resistant, adherent coating thereon.

14. A process of coating a metal surface comprising the steps of filming on the metal surface a composition in which the resin, oil and solvent constituents consist essentially of (I) copolymer selected from copolymers of vinyl chloride and vinylidene chloride in proportions of 30/70 to 75/25, inclusive, and mixtures thereof, and characterized by complete solubility in xylene at 25% solids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25 C. in 0.4% solution in nitrobenzene; (II) solvent of which at least 85% consists of liquid aromatic hydrocarbon material having a boiling point at least as high as benzene, the balance of the solvent consisting of methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, ethyl acetate, butyl propionate, and mixtures thereof; and (III) an oleoresinous varnish base which consists of drying oil heated with oil-soluble, non-heat hardening varnish resin,

' which has a drying oil/varnish resin ratio in the range of 20/80 to 67/33, inclusive, and which is compatible in solution in said solvent with the said copolymer constituent but is capable of stratifying toward a metal surface when the composition is filmed on said surface; the combined solids concentration of the copolymer and oleoresinous varnish base in the solvent being in the range of 15 to 50%, inclusive, by weight and the ratio of the co polymer tothe oleoresinous varnish base on a solids basis being substantially 90/10; and baking the filmed composition on the metal surface at a temperature of 13 at least 260 F. to form a strong, resistant, adherent coating thereon.

15. A process of coating a metal surface comprising the steps of filming on the metal surface a composition in which the resin, oil and solvent constituents consist essentially of (I) copolymer selected from copolymers of vinyl chloride and vinylidene chloride in proportions of 30/70 to 75/25, inclusive, and mixtures thereof, and characterized *by complete solubility in xylene at 25 solids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25 C. in 0.4% solution in nitrobenzene; (H) solvent of which at least 85% consists of liquid aromatic hydrocarbon material having a boiling point at least as high as benzene, the balance of the solvent consisting of methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, ethyl acetate, butyl propionate, and mixtures thereof; and (III) an oleoresinous varnish base which consists of tung oil heated at substantially 350 F. for approximately 3 hours with oil-soluble, non-heat hardening para-phenyl phenol/formaldehyde resin, which has a drying oil/varnish resin ratio of substantially 50/50, and which is compatible in solution in said solvent with the said copolymer constituent but is capable of stratifying toward a metal surface when the composition is filmed on said surface; the combined solids concentration of the copolymer and oleoresinous varnish base in the solvent being in the range of 15 to 50%, inclusive, by weight, and the ratio of the copolymer to the oleoresinous varnish base on a solids basis being in the range of 95/5 to. 10/90, inclusive; and baking the filmed composition on the metal surface at a temperature of at least 260 F. to form a strong, resistant, adherent coating thereon.

16. A process of coating a metal surface comprising the steps of filming on the metal surface a composition in which the resin, oil and solvent constituents consist essentially of (I) copolymer of vinyl chloride and vinylidene chloride in proportions of substantially 60/40 and characterized by complete solubility in xylene at 25% solids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25 C. in 0.4% solution in nitrobenzene; (H) solvent of which at least 85% consists of liquid aromatic hydrocarbon material having a boiling point at least as high as benzene, the balance of the solvent consisting of methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, ethyl acetate, butyl propionate, and mixtures thereof; and (III) an oleoresinous varnish base which consists of drying oil heated with oil-soluble, non-heat hardening varnish resin, which has a drying oil/varnish resin ratio in the range of /80 to 67/33, inclusive, and which is compatible in solution in said solvent with the said copolymer constituent but is capable of stratifying toward a metal surface when the composition is filmed on said surface; the combined solids concentration of the copolymer and oleoresinous varnish base in the solvent being in the range of 15 to 50%, inclusive, by weight, and the ratio of the copolymer to the oleoresinous varnish base on a solids basis being in the range of 95/5 to 10/90, inclusive; and baking the filmed composition on the metal surface at a temperature of at least 260 F. to form a strong, resistant, adherent coating thereon.

17. A process of coating a metal surface, comprising the steps of filming on the surface a composition in which the resin, oil and solvent constituents consist essentially of (I) copolymers of vinyl chloride and vinylidene chloride in a ratio of substantially 60/40 and characterized by complete solubility in xylene at solids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25 C. in a 0.4% solution in nitrobenzene; (II) solvent selected from the group consisting of benzene, toluene, xylene and mixtures thereof; and (III) an oleoresinous varnish base consisting of substantially equal proportions of tung oil and para phenyl phenol/ formaldehyde heated together at substantially 350 F. for approximately 3 hours; the combined solids concentration of the copolymer and oleoresinous varnish base in the solvent being in the range of 15 to 50%, inclusive, by weight, and the ratio of the copolymer to the oleoresinous varnish base on a solids basis being in the range of 95/5 to 10/90, inclusive; and baking the filmed composition on the surface at -a temperature of at least 260 F. to form a strong, resistant, adherent coating thereon.

18. A process of coating a metal surface, comprising the steps of filming on the surface a composition in which the resin, oil and solvent constituents consist essentially of (I) copolymers of vinyl chloride and vinylidene chloride in a ratio of substantially 60/40 and characterized by complete solubility in xylene at 25 solid-s concentration and by specific viscosity of substantially 0.12

to 0.30 determined at 25 C. in a 0.4% solution in nitro-- benzene; (II) solvent selected from the group consisting of benzene, toluene, xylene and mixtures thereof; and (III) an oleoresinous varnish base consisting of substantially equal proportions of tung oil and para-phenylv phenol/formaldehyde heated together at substantially 350 F. for approximately 3 hours; the combined solids concentration of the copolymer and oleoresinous varnish base in the solvent being in the range of 15 to 50%, inclusive, by weight, and the ratio of the copolymer to the oleoresinous varnish base on a solids basis being substantially 90/10; and baking the filmed composition on the surface at a temperature of at least 260 F. to form a strong, resist-ant, adherent coating thereon.

19. A process of coating a tinplate surface, comprising the steps of filming on the 'tinplate surface a composition in which the resin, oil and solvent constituents consist essentially of (I) copolymers of vinyl chloride and vinylidene chloride in a ratio of substantially 60/40 and characterized by complete solubility in xylene at 25 solids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25 C. in a 0.4% solution in nitrobenzene; (II) solvent selected from the group consisting of benzene, toluene, xylene and mixtures thereof; and (III) an oleoresinous varnish base consisting of substantially equal proportions of tung oil and para-phenyl phenol/ formaldehyde heated together at substantially 350 F. for approximately 3 hours; the combined solids concentration of the copolymer and oleoresinous varnish base in the solvent being in the range of 15 to 50%, inclusive, by weight, and the ratio of the copolymer to the oleoresinous varnish base on a .solids basis being in the range of 90/ 10 to 25/75, inclusive; and baking the filmed composition on the tinplate surface at a temperature of at least 320 F. to form a strong, resistant, adherent coating thereon.

20. A proces of coating a primed tin surface comprising the steps of filming on the said surface a composition in which the resin, oil and solvent constituents consist essentially of (I) copolymer selected from copolymers of vinyl chloride and vinylidene chloride in proportions of 30/70 to 75/25, inclusive, and mixtures thereof, and characterized by complete solubility in xylene at 25% solids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25 C. in 0.4% solution in nitrobenzene; (II) solvent of which at least consists of liquid aromatic hydrocarbon material having a boiling point at least as high as benzene, the balance of the solvent consisting of methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, ethyl acetate, butyl propionate, and mixtures thereof; and (III) an oleoresinous varnish base which consists of drying oil heated with oil-soluble, non-heat hardening varnish resin, which has a drying oil/ varnish resin ratio in the range of 20/80 to 67/33, inclusive, and which is compatible in solution in said solvent with the said copolymer constituent but is capable of stratifying toward a metal surface when the composition i filmed on said surface;

15 the combined solids concentration of the copolymer and oleoresinous varnish base in the solvent being in the range of 15 to 50%, inclusive, by weight, and the ratio of the copolymer to the oleoresinous varnish base on a solid basis being in the range of 95/5 to /90, inclusive; and baking the filmed composition on the said surface at a temperature of at least 260 F. to form a strong, resistant, adherent coating thereon.

21. A process of coating a bare tin surface comprising the steps of filming on the said surface a composition in which the resin, oil and solvent constituents consist essentially of (I) copolymer selected from copolymers of vinyl chloride and vinylidene chloride in proportions of 30/70 to 75/25, inclusive, and mixtures thereof, and characterized by complete solubility in xylene at 25% solids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25 C. in 0.4% solution in nitrobenzene; (II) solvent of which at least 85% con sist of liquid aromatic hydrocarbon material having a boiling point at least as high as benzene, the balance of the solvent consisting of methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, ethyl acetate, butyl propionate, and mixtures thereof; and (III) an oleoresinous varnish base which consists of drying oil heated with oil-soluble, non-heat hardening varnish resin, which has a drying oil/varnish resin ratio in the range of 20/80 to 67/33, inclusive, and which is compatible in solution in said solvent with the said copolymer constituent but is capable of stratifying toward a metal surface when the composition is filmed on said surface; the combined solids concentration of the copolymer and oleoresinou varnish base in the solvent being in the range of to 50%, inclusive, by weight, and the ratio of the copolymer to the oleoresinous varnish base on a solids basis being in the range of 95 5 to 10/90, inclusive; and baking the filmed composition on the said surface at a temperature of at least 260 F. to form a strong, resistant, adherent coating thereon.

22. A process of coating a primed iron surface comprising the steps of filming on the said surface a composition in which the resin, oil and solvent constituents consist essentially of (I) copolymer selected from copolymers of vinyl chloride and vinylidene chloride in proportions of 30/70 to 75/25, inclusive, and mixtures thereof, and characterized by complete solubility in xylene at 25% solids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25 C. in 0.4% solution in nitrobenzene; (II) solvent of which at least 85 consists of liquid aromatic hydrocarbon material having a boiling point at least as high as benzene, the balance of the solvent consisting of methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, ethyl acetate, butyl propionate, and mixtures thereof; and (III) an oleoresinous varnish base which consists of drying oil heated with oil-soluble, non-heat hardening varnish resin, which has a drying oil/ varnish resin ratio in the range of /80 to 67/ 33, inclusive, and which i compatible in solution in said solvent with the said copolymer constituent but is capable of stratifying toward a metal surface when the composition is filmed on said surface; the combined solids concentration of the copolymer and oleoresinous varnish base in the solvent being in the range of 15 to 50%, inclusive, by weight, and the ratio of the copolymer to the oleoresinous varnish base on a solids basis being in the range of 95/5 to 10/90, inclusive; and baking the filmed composition on the said surface at a temperature of at least 260 F. to form a strong, resistant, adherent coating thereon.

23. A process of coating a bare iron surface comprising the steps of filming on the said surface a composition in which the resin, oil and solvent constituents consist essentially of (I) copolymer selected from copolymers of vinyl chloride and vinylidene chloride in proportions of 30/70 to 75/25, inclusive, and mixtures thereof, and characterized by complete solubility in xylene at solids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25 C. in 0.4% solution in nitrobenzene; (II) solvent of which at least 85 consists of liquid aromatic hydrocarbon material having a boiling point at least as high as benzene, the balance of the solvent consisting of methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, ethyl acetate, butyl propionate, and mixtures thereof; and (III) an oleoresinous varnish base which consists of drying oil heated with oil-soluble, non-heat hardening varnish resin, which has a drying oil/varnish resin ratio in the range of 20/80 to =67/ 33, inclusive, and which is compatible in solution in said solvent witth the said copolymer constituent but is capable of stratifying toward a metal surface when the composition is filmed on said surface; the combined solids concentration of the copolymer and oleoresinous varnish base in the solvent being in the range of 15 to inclusive, by weight, and the ratio of the copolymer to the oleoresinous varnish base on a solids basis being in the range of 95/5 to 10/90, inclusive; and baking the filmed composition on the said surface at a temperature of at least 260 F. to form a strong, resistant, adherent coating thereon.

24. A process of coating a primed aluminum surface comprising the steps of filming on the said surface a composition in which the resin, oil and solvent constituents consist essentially of (I) copolymer selected from copolymers of vinyl chloride and vinylidene chloride in proportions of 30/70 to /25, inclusive, and mixtures thereof, and characterized by complete solubility in xylene at 25% solids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25 C. in 0.4% solution in nitrobenzene; (II) solvent of which at least consists of liquid aromatic hydrocarbon material having a boiling point at least as high as benzene, the balance of the solvent consisting of methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, ethyl acetate, butyl propionate, and mixtures thereof; and (III) an oleoresinous varnish base which consists of drying oil heated with oil-soluble, non-heat hardening varnish resin, which has a drying oil/varnish resin ratio in the range of 20/80 to 67/33, inclusive, and which is compatible in solution in said solvent with the said copolymer constituent but is capable of stratifying toward a metal surface when the composition is filmed on said surface; the combined solids con-v centration of the copolymer and oleoresinous varnish base in the solvent being in the range of 15 to 50%, inclusive, by weight, and the ratio of the copolymer to the oleoresinous varnish base on a solids basis being in the range of /5 to 10/90, inclusive; and baking the filmed composition on the said surface at a temperature of at least 260 F. to form a strong, resistant, adherent coating thereon.

25. A process of coating a bare aluminum surface comprising the steps of filming on the said surface a composition in which the resin, oil and solvent constituents consist essentially of (I) copolymer selected from copolymers of vinyl chloride and vinylidene chloride in proportions of 30/70 to 75/25, inclusive, and mixtures thereof, and characterized by complete solubility in xylene at 25 solids concentration and by specific viscosity of substantially 0.12 to 0.30 determined at 25 C. in 0.4% solution in nitrobenzene; (II) solvent of which at least 85% consists of liquid aromatic hydrocarbon material having a boiling point at least as high as benzene, the balance of the solvent consisting of methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, ethyl acetate, butyl propionate, and mixtures thereof; and (III) an oleoresinous varnish base which consists of drying oil heated with oil-soluble, non-heat hardening varnish resin, which has a drying oil/varnish resin ratio in the range of 20/80 to 67/33, inclusive, and which is compatible in solution in said solvent with the said 17 18 eopolymer constituent but is capable of stratifying toward surface at a temperature of at least 260 F. to form a metal surface when the composition is filmed on said a strong, resistant, adherent coating thereon. surface; the combined solids concentration of the copolymer and oleoresinous varnish base in the solvent References Cited in the file of this patent being in the range of 15 to 50%, inclusive, by weight, 5 and the ratio of the copolymer to the oleoresinous varnish UNITED STATES PATENTS base on a solids basis being in the range of 95/5 to 10/90, 2,380,456 Maier et a1. July 31, 1945 inclusive; and baking the filmed composition on the said 2,384,885 Britton et al. l Sept. 18, 1945 

11. A PROCESS OF COATING A METAL SURFACE COMPRISING THE STEPS OF FILMING ON THE METAL SURFACE A COMPOSITION IN WHICH THE RESIN, OIL AND SOLVENT CONSTITUENTS CONSIST ESSENTIALLY OF (1) COPOLYMER SELECTED FROM COPOLYMERS OF VINYL CHLORIDE AND VINYLIDENE CHLORIDE IN PROPORTIONS OF 30/70 TO 75/25. INCLUSIVE, AND MIXTURES THEREOF,A ND CHARACTERIZED BY COMPLETE SOLUBILITY IN XYLENE AT 25% SOLIDS CONCENTRATION AND BY SPECIFIC VISCOSITY OF SUBSTANTIALLY 0.12 TO 0.30 DETERMINED AT 25*C. IN 0.4% SOLUTION IN NITROBENZENE; (22) SOLVENT OF WHICH AT LEAST 85% CONSISTS OF LIQUID AROMATIC HYDROCARBON MATERIAL HAVING A BOLILING POINT AT LEAST AS HIGH AS BENZENE, THE BALANCE OF THE SOLVENT CONSISTING OF MATERIAL SELECTED FROM THE GROUP CONSISTING OF METHYL ETHYL KETONE, METHYL ISOBUTYL KETONE, CYCLOHEXANONE, ETHYL ACETATE, BUTY PROPIONATE, AND MIXTURES THEREOF; AND (III) AN OLERESINOUS VARNISH BASE WHICH CONSISTS OF DRYING OIL HEATED WITH OIL-SOLUBLE, NON-HEAT HARDENING VARNISH RESIN, WHICH HAS A DRYING OIL/VARNISH RESIN RATIO IN THE RANGE OF 20/80 TO 67/33, INCLUSIVE, AND WHICH IS COMPATIBLE IN SOLUTION IN SAID SOLVENT WITH THE SAID COPOLYMER CONSTITUENT BUT IS CAPABLE OF STRAIFYING TOWARD A METAL SURFACE WHEN THE COMPOSITION IS FILMED ON SAID SURFACE; THE COMBINED SOLIDS CONCENTRATION OF THE COPOLYMER AND OLEORESINOUS VARNISH BASE IN THE SOLVENT BEING IN THE RANGE OF 15 TO 50%, INCLUSIVE, BY WEIGHT, AND THE RATIO OF THE COPOLYMER TO THE OLEORESINOUS VARNISH BASE ON A SOLIDS BASIS BEING IN THE RANGE OF 95/5 TO 10/90, INCLUSIVE; AND BAKING THE FILMED COMPOSITION ON THE METAL SURFACE AT A TEMPERATURE OF AT LEAST 260*F. TO FORM A STRONG, RESISTANT, ADHERENT COATING THEREON. 